Charletta adjusts the dial on the remote device that controls the electrodes surgically inserted into her spinal column. Her left leg begins to twitch alarmingly. Her inability to climax during sexual intercourse, to remedy which is why she is taking part in the clinical trial of the Orgasmatron, remains unmoved. "But it's useful if I want to kick someone in the ass," she observes.

Welcome to Orgasm Inc, which has its British premiere next week as part of the Bird's Eye View festival. It is a wry and unsqueamish piece of film-making by the American documentary-maker Liz Canner, who has spent the best part of the last decade charting charted the race to market the first medical cure for female sexual dysfunction (FSD), and attempted to unpick the complex and often confounding ethical dilemmas that have accompanied it.

The very existence of clinically correctable FSD is contentious: the way drug companies convert disorders into disorders that can be remedied only with the regular purchase of their branded pill is a familiar story. Indeed, the 90s study that identified 43% of American women as suffering from this baggily defined dysfunction was found to have been conducted by psychologists with links to the drugs industry. A 2005 survey that came to similar conclusions about women in Europe and Asia was sponsored by Pfizer, manufacturer of Viagra. And, crucially, the success of treatment for FSD is fairly subjective. It cannot – unlike Viagra - be measured against a map of the Mull of Kintyre.

The fact is that cases of purely medical sexual dysfunction among women are rare. As Petra Boynton – the British sexual health academic who has nobly exposed the profit motive of the medicaliser – points out, there already exists a variety of means to help women: education, therapy, existing healthcare for related conditions, improving communication skills within intimate relationships. "All of these can be made available now, yet nobody pushes for this when arguing for a medical 'cure' some time in the future." Boynton is similarly dubious about the way pharmaceutical companies appropriated feminist language of empowerment and sexual-satisfaction rights in order to paint critics as prudish or somehow anti-women.

In Orgasm Inc, Canner traces the coinage of FSD to the Viagra-inspired expectation that the transformation of common female sexual difficulties into a drug-soluble disorder would equal a bonanza for shareholders. But when her subject, Charletta, newly liberated from her Orgasmatron (which, incidentally, has yet to make it to the market) intones with the wonder of the newly sighted, "Maybe sex in the movies is not normal," one becomes aware of a broader cultural displacement. Drug companies can't alone be responsible for a shift in the meaning of sexuality that has seen it commodified, marketised and individualised, measured against a scale so narrowly objective as to be oppressive; where desire is functional and instrumental rather than co-created by two people.

The latest reporter on the pornification of society is the former home secretary Jacqui Smith, whose investigation for Five Live this week appeared to trade on her naivety as a legislator of hardcore material who had never seen the stuff, and a wife whose spouse was enjoying the milder end of the spectrum. But her anxieties about young people's access to and experience of online pornography are entirely valid. "Porn isn't sex education," she wrote in a pre-publicity piece. "But there are young people today growing up with the idea that it is. (And little wonder, given the woefully inadequate provision in their schools.) This is changing the way young people think about each other and what they expect to have to do in their sex lives."

I'd argue that the genders have always been socialised to experience their sexuality differently, with girls taught from an early age that sex is part of a romantic narrative of love, partnership and children, while boys are told that it is a discrete act underpinning masculinity. But porn deepens and distorts this divide. Boys learn to be consumers, viewing women as disposable and catering to their needs only. The concurrent lesson is that girls should value their sexuality only according to how it is perceived by men, denying their own needs in the process.

But as Zoe Margolis – the sex blogger and author of Girl with a One-Track Mind – argues, porn doesn't become mainstream in a vacuum. "[This] requires a much wider commodification … female sexuality packaged up as a product geared to generate profit: capitalism with tits, basically." The irony is that the apparent "anything goes" democratisation of desire in reality constrains men and women more than ever.

Just as Orgasm Inc argues that treating sexual problems is more complex than finding the female equivalent of a chemically sustained erection, challenging the wider commodification of sexuality is not zero-sum. This is not about a reactionary attempt to replace one stereotyped version (male, porny, penetrative) with another (female, cuddly, politically correct). But sex embodies a human freedom the market denies. To desire and be desired can be many things: funny, awkward, transforming, sacred and profane. To be honest about what turns you on, for a moment or a lifetime, demands a particularly intimate bravery that is threatened with extinction by the megaphone of cultural sexism.